This invention relates to a well screen used for a horizontal or high-angle well and, more particularly, to this type of well screen capable of preventing damage to the screen or deformation of slits of the screen which tends to occur when the screen passes through a bent portion of the well in forcing the screen through this type of well.
There is an increasing tendency in the field of wells for collecting oil, water, etc. to using, instead of a vertical well which is formed by vertically digging the ground from the ground surface toward an oil or water stratum, a horizontal or high-angle well which, as shown in FIG. 4, is formed by digging a vertical section 1a, a bent section 1b and a horizontal or high-angle section 1c extending horizontally or obliquely along an oil or water stratum 2. Such horizontal or high-angle well is advantageous in that, since a screen portion of such horizontal or high-angle well from which oil or water can be collected has a length as many times as a vertical well, such horizontal or high-angle well has an oil or water production efficiency as many times as a vertical well.
A screen 3 used in the horizontal or inclined well 1 has a vertical pipe section 3a extending from the ground surface to the oil or water stratum 2, a bent screen section 3b and a horizontal or high-angle screen section 3c extending horizontally or obliquely along the oil or water stratum. In setting this screen 3 in the well 1, a straight-line screen is gradually forced into the well 1 from the ground surface and the screen is bent from the vertical section 1a of the well 1 in conformity with the configuration of the well 1 and the horizontal or high-angle section 3c is thereby formed.
In such horizontal or high-angle well 1, the screen sections 3b and 3c of the straight-line screen which is forced into the well 1 are sequentially bent when the screen portion of these sections 3b and 3c pass through the bent section 1b of the well 1 and the horizontal section 3c is elastically restored to the straight-line configuration after passing through the bent section 1b of the well 1. The screen wire of the screen 3, however, is forcibly bent by sliding along the bent section 1b of the well 1 while it is pressed with a strong force against the wall surface of the bent section 1b and this often causes damage to the screen wire or causes plastic deformation of the screen wire which prevents restoration of the screen wire to the original configuration after the screen portion has reached the horizontal section 1c with the result that irregularity occurs in the width of the slits of the screen wire.
It is, therefore, an object of the invention to provide a well screen for a horizontal or high-angle well which is capable of effectively preventing damage to or plastic deformation of the screen which occurs when the screen passes through a bent section of the well.